This invention relates, in general, to an apparatus and method of testing pressure sensors, and more particularly, an apparatus and method of testing pressure sensors at low pressures.
Semiconductor pressure sensors are used to provide an electrical value indicative of the pressure being exerted on the sensor. The pressure sensor is typically comprised of a diaphragm and piezoresistive strain sensors positioned on or near the diaphragm which are connected in a circuit to measure the diaphragm deflection due to the pressure differential across the diaphragm.
Presently, pressure sensors are tested after final assembly of the devices. The devices are placed in a sealed pressure chamber that contains testing equipment. The pressure sensors are not only tested but calibrated using a laser trimming process. If the electrical properties measured from the device are high or low, resistors incorporated into the diaphragm are laser trimmed until the voltage is within the range for the given pressure.
This method is adequate for testing of high pressure devices at greater than approximately 10 kPa. However, the testing of low pressure sensors in this manner is both inaccurate and slow. The equipment used to test low pressure devices in the past utilized the modulation of a valve to supply a gas at low pressure to a sealed pressure chamber. This valve has induced instability at low pressures. Thus, a controllable, stable, low pressure test apparatus is needed for testing devices at 10 kPa and below. In addition, the procedure used in the past had a slow response time because the pressure needs to be stabilized over a period of approximately several minutes. This amount of time is unacceptable in high throughput manufacturing areas. Thus, it would be desirable to have a testing apparatus and process which improves the cycle time of those processes commercially available.